Scientists at The Scripps Research Institute have produced a powerful immune response in mice by incorporating an unnatural amino acid into a target protein. This novel approach could prove useful in the development of new vaccines for cancer, infectious diseases, and other disorders.

The study is being published this week in an advanced, online edition of the journal Proceedings of the National Academy of Sciences (USA).

"A major challenge in modern vaccinology is finding new ways to selectively induce a strong immune response to epitopes—the sites antibodies bind to," said Peter Schultz, a Scripps Research scientist and a member of the Skaggs Institute for Chemical Biology, whose laboratory led the research. "Our approach using unnatural amino acids could develop into a general method to generate a robust antibody response to host and foreign antigens in a number of important disease states."

In the new study, the scientists incorporated the unnatural amino acid, p-nitrophenylalanine (pNO2Phe), into the murine tumor necrosis factor-α (mTNF-α), a well characterized cytokine involved in the regulation of infectious, inflammatory, and autoimmune phenomena.

The scientists found that administration of the pNO2Phe-containing mTNF-α induced high levels of antibodies in mice whereas no significant immune response was observed for the naturally occurring counterpart. The antibodies generated against the pNO2Phe-containing mTNF-α were highly cross-reactive with the native protein, in other words, the generated antibodies against the modified protein also targeted the protein in its natural state. Moreover, these antibodies could also protect mice from death by septic shock. Septic shock, a potentially fatal condition, is known to involve the production and release of naturally occurring tumor necrosis factor.

The study noted that this cross-reaction occurred without the need for strong adjuvants (immune response accelerants) and resulted in high levels of antibodies that lasted as long as four months.

"Four month's duration for an antibody response is very long," Jan Grünewald said. "There are many other vaccines that have much shorter periods of significant antibody levels. This may help facilitate therapeutic applications of this methodology."

The scientists consider this study as a proof of principal, with implications that go well beyond diseases associated with mTNF-α, such as rheumatoid arthritis and Crohn's disease.

"There are a great many foreign or self-proteins that are associated with disease but are hardly recognized by the immune system," said Jan Grünewald. "When these proteins become active in certain disease states like cancer and malaria, you need to break this tolerance if you want to develop a workable vaccine. Our approach breaks tolerance in a novel way—with the unnatural amino acid pNO2Phe."

As a result of these new findings, the Schultz laboratory is now focused on applying this novel methodology to other protein targets. One is amyloid beta, a peptide considered to be the main cause of Alzheimer's disease; another is epidermal growth factor, which plays a key role in cancer development and progression.

Other authors of the study, "Immunochemical termination of self-tolerance," include Meng-Lin Tsao, Roshan Perera, Frank Niessen, Diane M. Kubitz, Vaughn V. Smider, Wolfram Ruf, and Richard A. Lerner of The Scripps Research Institute; and Liqun Dong, Ben G. Wen and Marc Nasoff of the Genomics Institute of the Novartis Research Foundation.

The study was supported by the National Institutes of Health, the Skaggs Institute for Chemical Biology, the Alexander von Humboldt Foundation, and the Deutsche Forschungsgemeinschaft.